Heavy petroleum streams, such as fractions of jet fuels, Fischer-Tropsch (“FT”) synthesis products, and FCC Light Cycle Oil (“LCO”), have a relatively low value. It would be very useful to find an economical way to upgrade such heavy streams.
Catalytic hydrodealkylation/reforming using microporous, crystalline borosilicate molecular sieve based catalysts is a one-stage process for upgrading a heavy petroleum feed to more useful product(s) such as high octane gasoline and aromatics. The aromatics thus produced, such as BTX (benzene, toluene, xylenes), EB (ethylbenzene), naphthalene and alkylnaphthalenes (methylnaphthalenes, dimethylnaphthalenes, etc.), are valuable feedstreams for various chemical processes. In the one-stage hydrodealkylation/reforming process, the heavy hydrocarbons such as heavy alkylaromatic compounds are converted via the hydrodealkylation to lighter and useful components which form the aforesaid useful aromatics under the reforming conditions.
The conventional amorphous reforming catalysts, such as Pt—Re/Al2O3/Cl which is associated with a small amount of chloride as promoter of acidity, do not fulfill efficiently the aforesaid task, especially due to the catalyst deactivation which occurs when the feed is a heavy feed such as fractions of jet fuels, FT synthesis products, and LCO.
In attempts to develop environmentally benign reforming catalysts, it was discovered that Pt supported on K-exchanged zeolite L (Pt/K—L) and its derivatives such as Pt/BaK—L exhibit exceptional selectivity for the aromatization of n-hexane, as described in U.S. Pat. Nos. 4,104,320; 4,434,311; 4,447,316; 5,914,028. In addition, other investigators have found methods of using other zeolites such as mordenite, ZSM-5/-11 and silicalite as catalysts for various reforming processes. The use of these zeolite catalysts and processes are described, for example, in U.S. Pat. Nos. 3,546,102; 3,574,092; 3,679,575; 4,018,711; 4,347,394. However, all these zeolites including zeolite L (zeolites are defined as microporous, crystalline aluminosilicates) fail in reforming the heavy feeds such as fractions of jet fuels, FT synthesis products, FCC heavy gasoline and LCO. This is at least partially because of the catalyst instability with these heavy feeds and the sulfur intolerance of the catalysts.
Catalytic hydrocracking or hydrodealkylation over zeolite (aluminosilicate) based or amorphous catalysts is another way to upgrade heavy hydrocarbon feeds by converting them to high octane gasoline and BTX, as described in U.S. Pat. Nos. 4,919,789; 4,943,366; 5,001,296; 5,043,513; 5,219,814; 5,401,389; 6,037,302; 6,114,268; 6,133,494. When compared to the catalytic hydrodealkylation/reforming process of the present invention, however, the hydrocracking/hydrodealkylation approach has at least three drawbacks. These drawbacks include: (1) some of the resulting non-aromatic products of hydrocracking/ hydrodealkylation are not further reconstructed or reformed to the useful BTX and naphthalene-related compounds because the process lacks in an integrated reforming function; (2) some of the resulting aromatic products are re-hydrogenated to their non-aromatic counterparts under the hydrocracking/hydrodealkylation conditions; and (3) high hydrogen consumption associated with the hydrocracking/hydrodealkylation chemistry.
Other investigators have found methods of upgrading the aforesaid heavy hydrocarbons via integrating the hydrocracking/hydrodealkylation and reforming in one process. For example, M. N. Harandi et al. (U.S. Pat. No. 5,409,595) teaches a process for converting C9+ containing heavy naphthas to gasoline products of reduced end boiling range and higher octane than the feed. They claim the process is suitable for making BTX. The process is two-stage. The first is a hydrocracking stage in which heavier components are converted to lighter products. The first stage uses zeolites for the cracking reactions, e.g., beta, ZSM4, ZSM-12, mordenite, etc. In the second stage, at least a portion of the resultant hydrocracking product from the first stage is then aromatized in a reforming section. The reforming uses typical reforming catalysts containing chlorine (HCl) as an acidity promoter. The disadvantages of this process are that it utilizes a two-stage approach and environmentally unfriendly reforming catalysts containing HCl. As mentioned above, the reforming catalyst used in the second stage is typically not capable of handling the heavy feeds. U.S. Pat. No. 5,080,776 (Partridge et al.) also discloses a similar two-stage hydrocracking-reforming process.
L. L. Breckenridge and C. L. Markham (U.S. Pat. No. 4,906,353) claim a process which includes reforming a sulfur, nitrogen and/or olefin containing feed, e.g., an FCC gasoline, using noble metal containing large pore zeolites (aluminosilicates) having Constraint Indexes below 2 and a framework molar SiO2/Al2O3 ratio of at least about 50. The given examples of such zeolites are zeolite Beta, zeolite L, faujasite, mordenite, ZSM-3, ZSM-4, ZSM-18 and ZSM-20. The process can reportedly be operated in two modes, namely reforming and hydrocracking, to offer the refiner increased operation flexibility in meeting rapidly fluctuating changes in demand for high octane gasoline and LPG (Liquid Petroleum Gas) products. When compared with the borosilicate molecular sieve based catalysts of our present invention to be described below, the zeolite (aluminosilicate) catalysts applied in the above process (U.S. Pat. No. 4,906,353) contribute favorably to hydrocracking and hydrodealkylation due to the inherent strong acidity of zeolites.
As reported in U.S. Pat. Nos. 4,859,442; 5,106,801; 5,187,132; 5,202,014; 5,215,648; 5,591,322; 5,653,956 (Zones et al.), recently a series of novel microporous, crystalline borosilicate molecular sieves (defined herein as borosilicate molecular sieves to differentiate from zeolites which are microporous, crystalline aluminosilicates) has been successfully synthesized. Examples are SSZ-24, SSZ-25, SSZ-31, SSZ-33, SSZ-35, SSZ-37, SSZ-42, SSZ-43, SSZ-44, SSZ-47, SSZ-48, CIT-5, UTD-1 and/or and low-aluminum boron-beta (B-beta). This class of molecular sieves possesses lower acidity than zeolites (aluminosilicates). When zeolites (aluminosilicates) are used as reforming catalysts, their highly acidic framework is usually neutralized by using alkali and/or alkaline-earth cations in order to reduce the acidity to a very low level with a target of eliminating the undesirable hydrocracking reactions, as demonstrated by Pt/BaK—L. With their lower acidity properties, borosilicate molecular sieves provide a new class of catalyst materials for catalytic reforming. Zones et al. (U.S. Pat. No. 5,114,565, and in Advanced Catalytic Materials-1996, edited by P. W. Lednor et al., publisher: Materials Research Society) have already demonstrated that large pore borosilicate molecular sieves are useful catalysts for reforming hydrocarbon feedstreams such as naphtha. In addition, previous work by Klotz (U.S. Pat. No. 4,269,813) has also shown the value of using intermediate pore borosilicate molecular sieves for aromatics processing. Similarly, the use of some borosilicate zeolites having a Constraint Index between 1 and 12 (such as ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and zeolite beta) for catalytic reforming and other reactions is described in European Patent Application No. 188,913. It would be beneficial to have a process which employs novel borosilicate molecular sieves as catalysts to provide a new, economical and effective process for upgrading heavy petroleum streams containing larger molecules to high octane gasoline and valuable aromatics. We have found that the use of some novel microporous, crystalline borosilicate molecular sieves provides such a process. Preferred embodiments of the process of the invention are described below.